In conventional practice, there are inkjet recording apparatuses that record images by ejecting ink onto various recording mediums. Inkjet systems are capable of high-density and high-speed recording operations. Therefore, inkjet recording apparatuses have been applied and commercialized as printers, portable printers, and other apparatuses that serve as the output media of various apparatuses.
Generally, an inkjet recording apparatus is equipped with a carriage for mounting a recording means (recording head) and an ink tank, a conveying means for conveying the recording medium, and a control means for controlling these components. The recording head, which ejects ink droplets from a plurality of ejection ports, is serially scanned in a direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording paper, and the recording medium is intermittently conveyed by an amount equal to the recording width (or an amount less than the recording width) when recording is not taking place.
Such inkjet systems have low running costs because they record images by ejecting ink in necessary amounts onto a recording paper according to recording signals. Inkjet systems are also quiet recording systems because they record images on a recording medium without contact. Many products used in color recording apparatuses have also been put into practice because of their advantages in being able to easily record in color by using a plurality of ink colors.
In color inkjet recording apparatuses that use a plurality of color inks, black ink is often used for printing characters and the like. Therefore, images printed with black ink require printing sharpness, clarity, and high printing concentration. In view of this, there are known techniques for reducing the permeability of black ink on the recording medium and preventing the coloring material in the black ink from permeating through the recording medium.
With color ink, when two inks of different colors are deposited on the recording medium adjacent to each other, the inks of different colors mix together at their borders, resulting in a phenomenon (bleeding) in which the quality of the color image is reduced. In order to prevent such a phenomenon, known techniques are used for increasing the permeability of color ink on the recording medium and preventing color inks from mixing together on the surface of the recording medium (for example, Japanese Patent Application Laid-Open No. S55-65269).
However, when the inkset described above is used, the following two problems occur.
The first problem is that the recording medium is stained because it takes a long time for black ink to become fixed. Specifically, although color ink has high permeability and therefore a short fixing time, black ink has low permeability and therefore a long drying and fixing time. The result is that when the next page is successively ejected following ejection of the previous page, a condition is established in which the black ink on the previous page has not completely dried. When such a condition occurs, sometimes either the printed surface of the previously printed page or the reverse surface of the subsequently printed page is stained (this staining of the printed surface and reverse surface is hereinafter referred to as “smearing”). This problem becomes more severe at higher printing speeds.
The second problem is image degradation occurring at the borders between images of black ink and images of color ink. Specifically, since black ink has low permeability, blurring (border bleeding) occurs at the border areas between black and color inks in images where black and color inks come in contact. This is a problem that significantly reduces the quality of images recorded in color.
Hitherto, the following measures have been used to resolve these two problems.
The first measure is a method of providing a heating and fixing unit or another such fixing means. For example, Japanese Patent Application Laid-Open No. H08-132724 discloses a recording apparatus with an inkjet system that includes a heating and fixing unit. Using the heating and fixing unit to quickly fix the ink on paper makes it possible to prevent smearing and border bleeding.
The second measure is a method for the queue control of paper ejection. In this method, either the printing of the second page is temporarily halted, or the ejection of the second page is temporarily halted after printing is completed. This is done in the time it takes for one page to be printed and sufficiently dried. The occurrence of smearing can thereby be prevented. For example, Japanese Patent Application Laid-Open No. H07-205416 discloses a configuration wherein the printed image is identified for the already-printed recording medium, and the standby time is set for the printing of the next recording medium.
The third measure is a method of depositing color ink with high permeability over the areas in which black ink is to be deposited. Black ink is deposited on the surface of paper that is already coated by color ink. Therefore, the black ink is easily fixed on the paper surface, and smearing can be prevented. Furthermore, border bleeding can be prevented by using a type of inkset in which black and color inks react and coalesce.
However, the measures described above have had the following problems.
The problem with the first measure is that the recording apparatus must be provided with a fixing means, which leads to increases in the size and cost of the apparatus. Also, since serial printers feed paper intermittently, there is a possibility that the fixing means will not be uniformly effective in various areas of the recording medium when the medium is passed through areas in which the fixing means can be active.
The problem with the second measure is that printing throughput is reduced because of the need to temporarily halt the ejection of printed recording mediums and to set aside a standby time during printing.
The problem with the third measure is that black images deteriorate in sharpness and black characters deteriorate in quality because color ink and black ink are printed overlapping each other. Also, it has been difficult to prevent both smearing and border bleeding when the amount of color ink needed to prevent smearing differs from the amount of color ink needed to prevent border bleeding.